1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a multi-frequency ultrasonic cleansing method for a glass substrate of a TFT-LCD (Thin-Film Transistor Liquid Crystal Display).
2. The Related Arts
In a manufacture process of a TFT-LCD, when particles that have a size of around ⅓ of line width exist on a surface of a glass substrate, the occurrence of defects of for example short line or shorting becomes more frequent. To overcome such a problem, after a surface of a glass substrate has been processed by supplying a predetermined processing liquid, a cleansing operation is carried out on the glass substrate.
A conventional process that is currently adopted in the TFT-LCD industry to cleanse glass substrates is as follows. Plasma cleansing or extreme ultraviolet (EUV) cleansing or deep ultraviolet (DUV) cleansing is first applied, bushing, showering, and jet cleansing are then taken, and finally, two-fluid cleansing is carried out. The substances removed by these processes are respectively organic remains and particles and the sizes of the particles removed by these processes are respectively more than 10 μm, 1-10 μm, and 1-5 μm.
With the technical development trend of enlarged panel size, increased aperture ratio, and low line width, removing particles of various sizes by using the conventional machines shows the following drawbacks:
(1) Multiple machines must be used to respectively remove particles of different sizes and this requires a high expenditure for the machines and further, time is waste for substrates may be transferred among various machines and new particles may be introduced during the transfer of the substrates; and
(2) The generally principle of cleansing carried out by the machines is physical flushing, which gives no good result for cleansing particles having smaller size and securely stuck to the substrate and further, these cleansing operations use a large amount of distilled water and added solvents, leading to an increase of cost.
To improve the result of cleansing, ultrasonic cleansing is increasingly applied in the manufacture process of TFT-LCD. Ultrasonic cleansing is a cleansing process that is applied to the fields of precision machinery and specific precision mechanism. The ultrasonic cleansing uses cavitation effect induced by ultrasonic waves. Cavitation is implosion of tiny bulbs in a solution and is induced by variation of pressure within an ultrasonic field. Pressure difference is caused by alternation of positive and negative pressures in a liquid zone. When the liquid is in negative pressure, the boiling point is lowered, making it generating a number of tiny vapor bulbs. When the pressure turns positive, violent implosion occurs in the tiny bulbs. High frequency electrical energy released from a transducer generates mechanical waves. Such a cavitation phenomenon provides an effect of mechanical stirring and cleansing. The application of ultrasonic cleansing technique, to quite an extent, improves the result of cleansing a glass substrate of TFT-LCD. However, machines of different frequencies must be used for removal of particles of different sizes. This leads to a high expenditure of machine cost. Further, transferring substrates among various machines is a waste of time and may introduce new particles during the transfer process.